Alex
Just expanding on what Joerg wrote, you'll want to edit the hosts file on you 98 box to include the name and address of your ACS server. The file is usually located under C:/Windows/System, and may be called hosts.sam. You'll need to rename this file to 'hosts' and then edit itto include the IP Address and name of your acs server. you should be able to drop to a command prompt and type 'ping acsservername' and receive a response, where acsservername is the name of the server.
What may be happening is that you are accessing the server by IP address initally which means you load the login page fine, the user-login.tcl file actually uses the hostname of the ACS machine which your 98 machine knows nothing about, and so when your browser tries to redirect to the hostname, it fails giving you the errors you are seeing.
Hope this helps.
Cheers
